How is he supposed to do what he does best with such a short amount of time? Give him a chance!
This is the playoffs...in the playoffs, bench guys can't be given a long leash to be "given a chance".
Powe has been given a chance throughout the first two series (and game 1). Through that time, he has had 1 good game (against Atlanta). The rest of the time, he has given the team nothing on offense, and has been constantly missing the play on defense.
Big Baby has been inconsistent, but he at least makes the right rotation more times than not. Considering neither of them is giving them anything on offense, you have to go with Baby, because of his better understanding defensively.
Although what they really need to do is go with a 3 man big rotation, as others have pointed out.